Method for the decomposition of halogenated organic compounds in a contaminated medium

ABSTRACT

A method for the decomposition of halogenated organic compounds contained in a contaminated medium comprises adding an alkali metal carbonate or bicarbonate to the contaminated medium in an aqueous solution or in a solvent having a boiling point of at least 200° C., or in the form of a solid dispersion or suspension. The medium is heated to dehydrate the medium and then is further heated at a temperature between about 250° and 400° C. to effect decomposition of the halogenated organic compounds. An acid is then added to the medium in an amount sufficient to neutralize the same.

FIELD OF THE INVENTION

The present invention relates to a method for the decomposition ofhalogenated organic compounds contained in a contaminated medium. Moreparticularly, the invention relates to a method for the decompositionand removal of halogenated organic compounds contained in a contaminatedmedium by use of an alkali metal carbonate or bicarbonate.

BACKGROUND OF THE INVENTION

The hazards to public health and the environment which are posed by avariety of synthetic halogenated organic compounds are well known.Compounds such as polychlorinated biphenyls (PCB's), dibenzodioxins,dibenzofurans, dichlorodiphenyl trichloroethane (DDT), dieldrin, lindaneand chlordane, as well as other halogenated pesticides, have been foundto be persistent, environmentally toxic materials which require safe andefficient means of disposal. PCB's pose a particularly serious disposalproblem. Once widely used as dielectric fluid additives in electricalequipment such as transformers and capacitors because of their excellentinsulating properties, the use of PCB's in many applications has beenbanned by the U.S. Environmental Protection Agency owing to thecumulative storage of PCB's in the human body and the extremely hightoxicity of PCB's. Thus, methods for the removal and/or destruction ofhalogenated organic compounds such as PCB's are required.

Various methods for the removal and/or the destruction or decompositionof halogenated organic compounds are known in the art. For example, thePeterson U.S. Pat. Nos. 4,447,541 and 4,574,013 disclose methods fordecontaminating soil which is contaminated with halogenated organiccompounds. The Peterson U.S. Pat. No. 4,447,541 discloses a process inwhich a reagent mixture of an alkaline constituent and a sulfoxidecatalyst (DMSO) are intimately mixed with soil contaminated with PCB's.The reagent mixture affects a desorption of the halogenated contaminantsfrom the soil and subsequently dehalogenates the contaminants. However,this process is disadvantageous in that the kinetics are relatively slowand therefore reduction of the PCB concentration to an acceptable levelrequires extended time periods ranging from weeks to months, the soilmust be completely dry for the destruction to take place, largequantities of the reagent are required, and the sulfoxide catalyst maypotentially transport contaminants prior to their destruction. ThePeterson U.S. Pat. No. 4,574,013 discloses a process wherein a heatedslurry of contaminated soil is treated with a mixture of an alkalineconstituent and a sulfoxide catalyst. However, this process is similarlydisadvantageous in that the sulfoxide catalyst may transportcontaminants into living systems, and the sulfoxide catalyst producesodorous compounds when heated to high temperatures and decomposes intocombustible byproducts under elevated temperature conditions. Thisprocess is also disadvantageous in that it requires large amounts ofreagents.

The Rogers et al U.S. Pat. No. 4,675,464 discloses a method for thechemical destruction of halogenated aliphatic hydrocarbons, and moreparticularly a method for the chemical destruction of ethylenedibromide. An alkali metal hydroxide is dissolved in an ethylene glycoland the resulting product is reacted with the halogenated hydrocarbon.Rogers et al further disclose that the reaction temperature should bemaintained at 30° C. or less to maintain the reaction products insolution.

The Rogers et al copending application Ser. No. 07/350,425 discloses amethod for the destruction of halogenated organic compounds in acontaminated medium wherein an aqueous solution containing from about0.1 to about 20 weight percent polyethylene glycol is added to acontaminated medium. An alkali metal hydroxide is also added to thecontaminated medium, and the contaminated medium is heated at atemperature and for a time sufficient to dehydrate the medium. Themedium is further heated at a temperature of between about 100° and 350°C. for a time sufficient to effect destruction of the halogenatedorganic compounds, and an acid is added to the medium in an amountsufficient to provide the medium with a pH of from about 7 to about 9.

The Pytlewski et al U.S. Pat. No. 4,400,552 discloses a method for thedecomposition of halogenated organic compounds which employs a reagentcomprising the product of the reaction of an alkali metal hydroxide witha polyglycol or a polyglycol monoalkyl ether, and oxygen. The Pytlewskiet al U.S. Pat. Nos. 4,337,368 and 4,602,994 disclose similar methods ofdecomposing halogenated organic compounds. Additionally, the Pytlewskiet al U.S. Pat. Nos. 4,430,208, 4,417,977, 4,460,797 and 4,471,143 alsodisclose methods for separation and/or decomposition of halogenatedorganic compounds. However, these methods are disadvantageous in thatexcess amounts of the alkali metal hydroxide and polyglycol reagents arerequired in order to obtain a homogeneous distribution throughout thecontaminated material, for example soil, sediment, sludge or the like,which is treated. The Pytlewski et al U.S. Pat. Nos. 4,349,380 and4,523,043 disclose the use of reagents made from an alkali metal oralkali metal hydroxide and a polyglycol or a polyglycol monoalkyl etherfor removing metals from metal-containing materials and for decomposingorgano sulfur compounds, respectively. Similarly, the Brunelle U.S. Pat.Nos. 4,351,718 and 4,353,793 disclose methods for removingpolyhalogenated hydrocarbons from nonpolar organic solvent solutions bytreating the contaminated solutions with a mixture of polyethyleneglycol and an alkali metal hydroxide. These methods are similarlydisadvantageous in that excess amounts of reagent are required.Additional methods for removing and/or destructing halogenated organiccompounds contained in contaminated materials are disclosed in theHoward et al U.S. Pat. No. 4,327,027, the Heller U.S. Pat. No.4,483,716, the Mendiratta et al U.S. Pat. No. 4,663,027, the Meenan etal U.S. Pat. Nos. 4,685,220 and 4,793,937, the Rossi et al U.S. Pat. No.4,761,221, the Zeff et al U.S. Pat. No. 4,792,407, European PatentApplication No. 118,858, Chemical Abstracts, Vol. 82, No. 139620P (1975)and Kornel et al, Journal of Hazardous Materials, 12 (1985), pages161-176. However, these and additional processes known in the art forthe removal and/or destruction of halogenated organic compounds incontaminated materials are inadequate in view of the time required foracceptable levels of removal and/or destruction, the use of excessiveamounts of various reagents, the use of expensive reagents, theproduction of toxic and/or combustible byproducts, and/or the failure toobtain desired removal and/or destruction levels. Thus, a need existsfor additional methods for the removal and/or destruction of halogenatedorganic compounds in contaminated materials, which methods overcome thedisadvantages of the prior art.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a newmethod for the decomposition and removal of halogenated organiccompounds contained in a contaminated medium. It is a further object ofthe invention to provide a method for the decomposition and removal ofhalogenated organic compounds contained in a contaminated medium whichemploys significantly less amounts of reagent and which employs lowercosting reagents, as compared with prior art methods. It is a furtherobject of the invention to provide such a method wherein environmentallyacceptable levels of halogenated organic compounds are achieved in thetreated materials. It is a related object of the invention to providesuch a method wherein the environmentally acceptable levels ofcontaminants in the materials are obtainable within a short period oftime.

These and additional objects are achieved by the present invention whichrelates to methods for the decomposition of halogenated organiccompounds contained in a contaminated medium. The methods of theinvention comprise the steps of adding an alkali metal carbonate orbicarbonate to a contaminated medium containing the halogenated organiccompounds. The alkali metal carbonate or bicarbonate may be in anaqueous solution which distributes the alkali metal compound throughoutthe medium and acts as a wetting agent, or in a solvent, or may be addedas a solid dispersion or suspension. The contaminated medium is thenheated at a temperature and for a time sufficient to dehydrate themedium. Although the water is removed, the alkali metal compound is welldistributed throughout the medium and is concentrated to a very reactivestate. The medium is then further heated at a temperature between about250° and 400° C. for a time sufficient to effect decomposition of thehalogenated organic compounds. Decomposition of the halogenatedcompounds in the contaminated medium is more dependent on the presenceof the alkali metal compound as the temperature increases within thisrange. Finally, an acid is added to the medium in an amount sufficientto neutralize the medium so that it may be returned to its originalenvironment. Because the aqueous solution or solvent is employed, theamount of alkali metal compound which is required for the presentmethods is significantly reduced as compared with prior art methods.Additionally, because the reagent is well distributed throughout themedium by the aqueous solution, a uniform destruction of the halogenatedorganic compounds is achieved. Moreover, because lower amounts ofreagent are employed, recycling of excess reagents is not required.Finally, the present methods are advantageous in the use of the alkalimetal carbonate or bicarbonate in that these compounds are lesscorrosive than the alkali metal hydroxides employed in prior art methodsand require less acid for neutralization.

These and additional objects and advantages will become more fullyunderstood in view of the following detailed description.

DETAILED DESCRIPTION

The present invention comprises methods for the decomposition andremoval of halogenated organic compounds contained in a contaminatedmedium. The contaminated medium may comprise soil, sludge, sediment or aliquid. The present methods are particularly adapted for use with soils,sludges and sediments. The methods are suitable for use with mediumswhich contain up to 100,000 ppm of halogenated organic compounds,aliphatic or aromatic, for example PCB's, or even higher levels of thehalogenated organic compounds. The contaminated mediums which aresuitable for use in the invention may also include an absorbent oradsorbent, for example spent activated carbon or the like. Additionally,the methods of the invention may be used for the treatment of purehalogenated materials, for example, aldrin, dieldrin and otherhalogenated pesticides.

Generally, the methods of the invention comprise adding an alkali metalcarbonate or bicarbonate, or a mixture thereof, to the contaminatedmedium containing one or more halogenated organic compounds. The alkalimetal carbonate or bicarbonate may be added to the contaminated mediumin an aqueous solution or in a high boiling solvent. Alternatively, thealkali metal carbonate or bicarbonate may be added in the form of asolid dispersion or suspension. When the alkali metal carbonate orbicarbonate is added in an aqueous solution, the water from the aqueoussolution assists in distributing the alkali metal compound homogeneouslythroughout the contaminated medium. Alternatively, when the alkali metalcarbonate or bicarbonate is added with a high boiling solvent, thesolvent component serves to extract the contaminates and to raise theirboiling points whereby the volatility of the pollutants is reduced andthe pollutants are retained in the reaction system for decomposition.The high boiling solvent also serves as a hydrogen donor to producedecomposition fragments of the toxic and hazardous pollutant compounds.Suitable solvents have a boiling point of at least 200° C., andpreferably from about 200° C. to about 500° C. Preferred solventsinclude hydrocarbon compounds. In an additional embodiment, the alkalimetal carbonate or bicarbonate compounds may be added to thecontaminated medium in an aqueous solution, wherein the aqueous solutionfurther contains a high boiling solvent.

The alkali metal carbonate or bicarbonate is added to the contaminatedmedium in an amount of from about 1 to about 20 weight percent, based onthe weight of the contaminated medium. The specific amount of alkalimetal compound which is required is dependent on the level ofhalogenated organic compounds contained in the contaminated medium. In apreferred embodiment, the alkali metal reagent is added in an amount offrom about 2 to about 12 weight percent based on the weight of thecontaminated medium. The metal which forms the carbonate or bicarbonatereagent may be any of the alkali metals, or mixtures thereof. Preferredalkali metals include lithium, sodium and potassium with sodium andpotassium being particularly preferred.

After addition of the alkali metal compound, the contaminated medium isheated at a temperature and for a time sufficient to totally dehydratethe medium, i.e., to remove 100 weight percent of the water containedtherein. This heating step may be performed at atmospheric pressure orat reduced or elevated pressures if so desired. As noted above, thewater which is included in the aqueous solution allows homogeneousdistribution of the alkali metal compounds throughout the medium andacts as a wetting agent and a penetrant. Moreover, when the water isremoved from the medium during the dehydration step, the reagent is thenconcentrated to a very reactive state yet is well distributed throughoutthe contaminated medium.

After dehydration, the medium is further heated at a temperature betweenabout 250° and 400° C. for a time sufficient to effect decomposition ofthe halogenated organic compounds. More preferably, the medium is heatedat a temperature between about 250° C. and 350° C. to effectdecomposition of the halogenated organic compounds. This step may beconducted at atmospheric pressure or at reduced or elevated pressures.The time required for decomposition of the halogenated organic compoundssimilarly depends upon the level of such compounds in the contaminatedmaterial. Generally however, a time period of from about 0.25 to about 4hours is sufficient.

In the methods of the present invention, the alkali metal carbonate orbicarbonate reacts with the halogenated organic compounds, for examplearomatics such PCB's, to initially form an alkali metal halide and apartially dehalogenated PCB structure. Upon further heating attemperatures above 250° C., a base catalyzed removal of the halogensoccurs together with reduction and decomposition of the remainingorganic compounds.

Finally, the medium is treated with an acid for neutralization.Preferably, the acid is added in amount sufficient to provide the mediumwith a pH value of from about 7 to about 9. Suitable acids for use inthe invention comprise sulfuric acid, phosphoric acid, hydrochloric acidand nitric acid. With the exception of hydrochloric acid, these acidsnot only neutralize the medium but also provide valuable soilfertilizers, for example Na₂ SO₄ or sodium sulfate from use of sulfuricacid, NaH₂ PO₄, Na₂ HPO₄, Na₃ PO₄ or sodium phosphates from the use ofphosphoric acid, and NaNO₃ or sodium nitrate from the use of nitricacid, given that sodium is employed as the alkali metal. If potassium isused, then the potassium salts are produced. The resulting medium maythen be safely returned to its original environment if desired.

Generally, oxygen is not a detriment to the methods of the presentinvention and therefore air need not be excluded. When applied to thedecontamination of hydrocarbon fluids, either aliphatic or aromatic, itmay be desirable to exclude air in order to prevent ignition of thehydrocarbon. Thus, the present methods may be performed either in thepresence or the absence of an oxygen-containing atmosphere.

Because the present methods employ relatively small amounts of alkalimetal reagents, and solvent if used, there is no need to recover excessreagents for reuse. Moreover, because the present invention employswater to wet the contaminated medium and to distribute the alkali metalreagents therein, the present methods are significantly less costly thanprior art methods which employ polyethylene glycol to wet thecontaminated medium. The present methods may be performed in either acontinuous or a batch system, and, if desired, all steps may beperformed in a single reactor. As will be demonstrated in the Examples,the methods of the invention decompose the halogenated organiccompounds, particularly haloaromatic and cyclic aliphatic compounds, tonondetectable levels. Additionally, the products of the present methodsare non-mutagenic, non-teratogenic and non-toxic to life forms.

The methods of the present invention are demonstrated in the followingExamples:

EXAMPLE 1

This example demonstrates the application of the methods according tothe present invention to a contaminated liquid material. Fifty ml of acontaminated solvent material containing 10% aldrin was mixed with anaqueous solution formed from 10 grams of sodium bicarbonate and 10 ml ofwater. The mixture was agitated by stirring and was heated to 290° to320° C. for approximately one to two hours. The aldrin concentrationrapidly fell to below detectable limits, thus resulting in analdrin-free solvent.

EXAMPLE 2

This example demonstrates the application of the methods according tothe present invention to treatment of contaminated soil. One hundredgrams of contaminated soil containing 2,200 ppm Aroclor 1260, 1,000 ppmAroclor 1242, 1,000 ppm of pentachlorophenol, 1,000 ppm of dieldrine and1,000 ppm of lindane were supplied to a chemical reactor system.Approximately 5 grams of sodium bicarbonate (5 weight percent of thecontaminated medium) and one ml of a high boiling point hydrocarbonsolvent were added to the soil in a solution of 20 ml of water. Theresulting mixture was slurried and heated such that the water containedin the system was distilled off. The reaction system was then furtherheated to a temperature of approximately 290° to 340° C. for a period offrom 0.25 to 1.5 hours. At about 0.25 hours and a temperature of 340°C., residuals in the soil were less than one ppm for all pollutants.

Thus, the methods of the present invention are advantageous for removinghalogenated organic compounds from a contaminated medium. The methods ofthe present invention employ relatively inexpensive reagents, namely,the alkali metal carbonates and bicarbonates, and optionally highboiling solvents. The reagents are employed in relatively small amountsas compared with methods of the prior art. Additionally, the alkalimetal carbonates and bicarbonates employed in the methods of the presentinvention are less corrosive than the alkali metal hydroxides employedin many prior art methods. Thus, the methods of the present inventionprovide an improved process for destroying haloaromatic and aliphaticcompounds to non-detectable levels. The products produced by the presentmethods are simple lower molecular weight materials, for example,hydrocarbons, alkanes, alcohols and the like, which are non-mutagenic,non-teratogenic and non-toxic to life forms.

The preceding examples are set forth to illustrate specific embodimentsof the invention, and are not intended to limit the scope of the methodsof the present invention. Additional embodiments and advantages withinthe scope of the claimed invention will be apparent to an ordinary skillin the art.

What is claimed is:
 1. A method for the decomposition of halogenatedorganic compounds contained in a contaminated medium, comprising(a)adding an alkali metal carbonate or bicarbonate to a contaminated mediumcontaining halogenated organic compounds, said alkali metal carbonate orbicarbonate being added as an aqueous solution or in a solvent having aboiling point of at least 200° C., or in the form of a solid suspension;(b) heating the contaminated medium at a temperature and for a timesufficient to substantially dehydrate the medium; (c) further heatingthe medium at a temperature between about 250° and 400° C. for a timesufficient to effect decomposition of the halogenated organic compounds;and (d) adding an acid to the medium in an amount sufficient to providethe medium with a pH of from about 7 to about
 9. 2. A method as definedin claim 1, wherein the alkali metal carbonate or bicarbonate is addedin an aqueous solution.
 3. A method as defined in claim 2, wherein theaqueous solution further contains a hydrocarbon solvent having a boilingpoint of at least 200° C.
 4. A method as defined in claim 1, wherein thealkali metal carbonate or bicarbonate is added in a solvent having aboiling point of at least 200° C.
 5. A method as defined in claim 4,wherein the solvent comprises a hydrocarbon compound.
 6. A method asdefined in claim 1, wherein the alkali metal carbonate or bicarbonate isadded as a solid suspension.
 7. A method as defined in claim 1, whereinthe alkali metal carbonate or bicarbonate is added in an amount of fromabout 1 to about 20 weight percent based on the weight of thecontaminated medium.
 8. A method as defined by claim 7, wherein thealkali metal carbonate or bicarbonate is added in an amount of fromabout 2 to about 12 weight percent based on the weight of thecontaminated medium.
 9. A method as defined in claim 1, wherein thealkali metal comprises sodium.
 10. A method as defined in claim 1,wherein the alkali metal comprises potassium.
 11. A method as defined inclaim 1, wherein the alkali metal comprises lithium.
 12. A method asdefined by claim 1, wherein the contaminated medium is heated undervacuum to dehydrate the medium.
 13. A method as defined by claim 1,wherein in step (c) the medium is further heated at a temperaturebetween about 250° C. and 350° C. to effect destruction of thehalogenated organic compounds.
 14. A method as defined by claim 1,wherein the acid which is added to the medium to provide a pH of from 7to about 9 is selected from the group consisting of sulfuric acid,phosphoric acid, hydrochloric acid and nitric acid.
 15. A method asdefined by claim 1, wherein the contaminated medium comprises soil. 16.A method as defined by claim 1, wherein the contaminated mediumcomprises sludge.
 17. A method as defined by claim 1, wherein thecontaminated medium comprises sediment.
 18. A method as defined by claim1, wherein the contaminated medium includes an absorbent comprisingspent activated carbon.
 19. A method as defined by claim 1, wherein thecontaminated medium comprises a liquid.
 20. A method as defined by claim1, wherein the contaminated medium contains up to 100,000 ppm ofhalogenated organic compounds.
 21. A method as defined by claim 1,wherein the contaminated medium comprises a pure halogenated material.22. A method as defined by claim 1, wherein the medium which resultsfrom the acid addition step is returned to its original environment.